At the center of the retina is the macula, from which we get sharp central vision. The retinal nerve fiber layer, which extends from the optic nerve to connect the eye to the brain, is a thin nerve cell layer that sends visual information to the brain. Recently, researchers in China and Australia have linked tea and coffee to brain and eye health. Learn more about their findings here.*

Can coffee and tea protect against neurodegeneration?

Some six billion tons of tea and 10 billion tons of coffee were consumed globally in 2021. Given their level of popularity, the researchers say in the journal Nutrients, public health should be “enormously” impacted by coffee and tea, whether positive or negative. Prior research shows that coffee and tea enthusiasts have lower Parkinson’s disease and dementia risks, but the evidence is limited. Nevertheless, scientists theorize that coffee and tea’s antioxidant plant nutrients may have neuroprotective benefits.

Since the retina is connected to the central nervous system, the researchers explain, it presents a unique, non-invasive window into brain health via optical coherence tomography (OCT), an advanced eye analysis tool. Through OCT, previous research has found strong links between:

• The thinning of the retinal nerve fiber layer (RNFL), 
• Cognitive decline, and 
• Neurodegenerative conditions like glaucoma, Parkinson’s disease, and Alzheimer’s disease. 

Using self-reported beverage intake and OCT measurements of the macula RNFL (mRNFL), the investigators could further explore coffee and tea’s potential neuroprotective properties.

What the researchers did

Led by Lisa Zhuoting Zhu, M.D., Ph.D., Principal Investigator of Ophthalmic Epidemiology at the Centre for Eye Research Australia (CERA), and Mingguang He, M.D., Ph.D., head of CERA’s ophthalmic epidemiology research, the team investigated associations between beverage consumption and mRNFL thickness.

Using data from the U.K. Biobank study, over 35,000 participants were questioned about average daily cups of coffee and tea during the past year. Participants were divided into four categories according to how much coffee or tea they drank daily:

• 0 cups per day
• 0.5-1 cup per day
• 2-3 cups per day
• 4 or more cups per day

What they found

After adjusting for outside factors, the researchers found positive associations between mRNFL thickness and coffee and tea, suggesting brain-protective potential.

• Coffee drinkers showed significantly increased thickness, especially at 2-3 cups per day.
• Tea drinkers also showed greatly increased thickness, especially at over 4 cups per day.

The “sweet spot” for coffee and mRNFL health is a medium amount of coffee, said Zhu. “Not too much and not too little.”

Other experts have suggested that one cup of caffeinated coffee per day is safe for people with glaucoma. If you have glaucoma, or are at risk for the disease, consult with your eye doctor before increasing consumption.

What it means

Zhu concludes that mRNFL thickness is a measure of both eye and brain health. “Our findings indicate if we consume two to three cups of coffee or more than four cups of tea per day, the macular thickness will increase.”

She cautions, however, that per her research, instant coffee may actually increase your risk for neurodegenerative diseases and other negative outcomes.

More research is needed to explore and explain these apparent connections. 

*Centre for Eye Research Australia. (2023, May 5). Study links drinking coffee and tea to increased macular retinal nerve fiber layer thickness. MDLinx. https://www.mdlinx.com/news/study-links-drinking-coffee-and-tea-to-increased-macular-retinal-nerve-fiber-layer-thickness/1B5JEvTFaVAmdtVdMZ7rDM